I. Technical Field of the Invention
This invention relates to aeronautics and particularly to fastening systems for fittings at the rear of trimmable horizontal stabilizers of an aircraft.
II. Description of the Related Art
The fastening of a trimmable horizontal stabilizer in an aircraft with a low tail is usually carried out by means of three points. So that the plane of the horizontal stabilizer can trim the one or two most forward fastening points, it has to change its position vertically by means of a spindle in such a way that the stabilizer pivots on the other two support points which can be referred to as pivot points.
In conventional systems, the fastening of the two rear pivot points of the stabilizer is basically done by means of two solutions, namely, by means of a fitting joined to the central core of the closing frame of the cut-out provided for the passage of the near end of the horizontal stabilizer, or by means of a fitting integral with the core of the closing frame and in the beam of the cut-out and two flat plates which transmit the loads from the stabilizer to the frame and to the beam.
According to the first of these conventional solutions, the loads pass directly from the horizontal stabilizer to the stiffened plate which constitutes the central part of the closing frame of the cut-out. The main drawback of this solution is the load eccentricity existing in the fitting due to supporting vertical loads, which means that counter-fittings have to be located on the other side of the frame. Another of the main problems is that the axial loads also have to pass to the covering by means of counter-fittings. All these counter-fittings greatly increase the weight of the solution and increase the assembly time.
Moreover, and according to the second of these solutions, the lateral loads of the stabilizer are transmitted to the frame by means of bars which are connected to the beam which stiffens the frame while the vertical loads and those in the axial direction are respectively transmitted to the frame and to the beams of the cut-out by means of plates and the fittings. The union lugs allow free rotation, which prevents the plates from transmitting moments to the fittings. The main disadvantage of this solution is the complexity which the fastening fittings for the plates add to the union node, in itself already complex, between the beam of the cut-out, the frame and the beam that stiffens the frame. This solution is also very complex when it comes to wanting to use a composite material for its manufacture, since the manufacture of a fastening fitting of this kind in a composite material is virtually impossible at present.